This invention relates to hydraulic control systems, and relates more particularly to pressure compensated type hydraulic control systems.
In certain applications of hydraulic power systems, pressure compensated variable displacement pumps have found utility by reducing the volume of flow discharged by the pump, and consequently the power required to operate the pump, whenever the hydraulic flow requirements are substantially reduced. In aircraft, for instance, the major demand upon the hydraulic system occurs during landing and takeoff when landing gear, flaps, etc. are operated. Throughout the remainder of the flight the hydraulic flow demand requirements are substantially lower. The pressure compensated pump automatically reduces its displacement in relation to the flow demand requirements to reduce the power consumed during this essentially "standby" condition. A drawback to such a system however is that the pump is still operating at a relatively high, constant, speed and significant standby power consumption by the pump still occurs. Examples of prior art hydraulic systems are found in U.S. Pat. No. 1,576,153; 1,863,406; 2,425,958; 2,694,979; 2,752,858; and 2,961,964.
It is a primary object of the present invention to provide an improved hydraulic power system and method which utilizes not only a pressure compensated pump to vary the flow developed by the pump in relation to the demand requirements of the hydraulic system, but which also substantially varies the rotational speed of the pump in relation to the demand requirements to significantly reduce the power consumed by the hydraulic system when operating at less than maximum power demand.
More particularly, it is an important object of the present invention to provide a pressure compensated pump which includes method and apparatus for sensing pump displacement and varying the input shaft speed to the pump in relationship to pump displacement.
These and other objects and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of preferred forms of the invention when read in conjunction with the accompanying drawing.